Meeting Maker has a nice auto pick feature which will go out and find the next time when all the potential invitees to a meeting are available, I do not see this in Zimbra, am I missing it or does it not exist?

There is a "Calendar Scheduler" zimlet that gives a vaguely Outlook WebAccess-ish weekly view of everyone's availability, with auto-pick and click-for-a-time. It's still flagged as "experimental" and it takes some trial and error to figure out the UI, but I've had it enabled for about a year.